1. Field of the Invention
The invention relates to a method of supplying oil from a first floating structure to an offloading structure, comprising the steps of:
providing a flexible duct extending between the two structures at a water depth of between 50 m and 500 m, the duct comprising a flexible elastomeric material and having an internal diameter of at least 600 mm and a length of between 1,500 and 3,000 m, and providing at least one pump at the first structure and pumping the oil through the duct at a pressure between 5 bar and 30 bar and at a flow rate between 1,000 and 50,000 m3/hr.
2. Description of the Related Art
Such flexible ducts are known from WO 02/44607, in which a marine hose is described which may have a length of 2 km or more, extending between an oil rig, FPSO, TLP, SPAR or Semi submersible, and an offloading buoy, such as a catenary anchor leg mooring (CALM) buoy, at depths between 80 and 30 meters. The known hose consists of 12-meter elastomeric segments with an internal diameter of 600 mm having end coupling flanges. The known duct is applied as a bundle of parallel ducts for increased capacity.
Rigid steel pipes are also used for transfer of crude oil, and generally have a diameter of 24″ such that multiple ducts are used in parallel for obtaining sufficient capacity. The transfer pipes extending horizontally below water level between the floating structure and the offloading buoy are supported by floaters. Due to the weight of the steel pipes and their limited flexibility, these steel pipes are subject to metal fatigue.
When hydrocarbons, such as oils are transported through the known mid-water transfer pipes, heat loss through these pipes results in increased viscosity of the hydrocarbons and reduced flow capacity.